It is known to use a heat exchanger in a gas turbine engine for heating fuel prior to combustion using heat contained within the high pressure air leaving the combustor or using heat contained within engine's oil system. The pressurised air/oil cooled within the heat exchanger is used to cool turbine components.
Various types of heat exchangers are known including tubular heat exchangers and plate/fin heat exchangers.
Tubular heat exchangers comprise a tubular shell through which a first fluid flows. The tubular shell may contain baffles for directing the flow of the first fluid along a convoluted path from an inlet to an outlet. A number of tubes (a tube bundle) carrying a second fluid extend from a tube manifold or tube sheet within the tubular shell so that heat exchange can occur between the first and second fluids through the walls of the tubes. Tubular heat exchangers are commonly used where one or both of the fluids is/are at a high pressure.
Plate/fin heat exchangers comprise a series of stacked plates sandwiching finned chambers which are enclosed at the edges by side bars. Separate first and second fluid streams flow through alternate chambers of the heat exchanger allowing heat transfer between the fluids in adjacent chambers. Plate/fin heat exchangers are suitable for use with high pressure fluids as the fins provide structural integrity to the structure.
Assembly and sealing of these known heat exchangers is typically by brazing. For example, in the tubular heat exchanger, the tubes of the tube bundle are connected to the tube manifold (which is enclosed within the tubular shell) by brazing and, in the plate/fin heat exchanger, the side bars are affixed by brazing. Failure of these brazed joints will lead to mixing of the two fluids which can be hazardous.
US 2012/0304662 describes a heat exchanger for a gas turbine engine comprising an annular duct housing two sets of inner and outer tubes. Two fuel conduits are defined between the inner and outer tubes with air conduits defined between the annular duct and the outer tubes and within the inner tubes. The inner and outer tubes defining the fuel conduits are sealed onto inlet and outlet end fittings using brazed joints. These brazed joints are in contact with the air conduit such that failure of the joint will lead to hazardous mixing of the fuel and compressed air.
The present invention aims to ameliorate the problems associated with the prior art.